Large land vehicles such as large trucks, commonly use air bags instead of springs to support an upper vehicle main part such as the vehicle chassis on a lower main part such as an axle, or to support a cab on the chassis. Like springs, the air bags absorb small vertical movements of the axles as the vehicle moves. For a proper ride, it is important that the air bag height be maintained close to the manufacturer's preferred height. At the selected height, the air bag pressure will also be optimum. An air bag requires a control to control the movement of pressured air at a pressure such as 120 psi, including the flow of air into an air bag when it is too short, and the flow of air out of the air bag when it is too tall.
One type of common control includes a valve with a rotatable valve member that can be rotated to any one of three positions within a housing to control the flow of air into or out of the air bag, or to prevent any air flow. The housing of the rotatable valve is fixed to one main vehicle part such as the chassis, and the rotatable valve member is connected to a linkage that consists of two links that connect to an axle. The linkage has the disadvantage that space must be left around the links, and the links constitute narrow elongated parts that can catch on clothing, cables, hoses, and other parts during vehicle repairs. A pressured air control for controlling air flow to and from an air bag, that could fit into the space between vehicle parts such as a chassis and axle occupied by prior controls, and which occupied little space and avoided long narrow parts that projected into otherwise empty space, would be of value.